Tannock,
R. (2013). Specific learning disabilities in DSM-5; Are the changes for
better or worse. The
International Journal for Research in Learning Disabilities, 1(2),
2-30.
This is
part B of a post discussing a document by Prof. Rosemary Tannock, a member of the DSM-5 Work-Group for ADHD and
Disruptive Behavior Disorders and a Liaison member of the Neurodevelopmental
Disorders Work Group to advise on Learning Disabilities. I'll continue
to present Prof. Tannock's views in
black or orange and my thoughts
in green.
In this
part, Prof. Tannock first tries to explain why the work group abandoned the
IQ-achievement discrepancy criterion for learning disabilities (LD) in
DSM5. Then she tries to explain why the
work group also waived the possibility to include cognitive processing deficits as a criteria for LD.
According to the IQ –
achievement discrepancy model, an LD child is a child with poor achievement in
reading/writing/mathematics and a full scale IQ that is average or above
average. Thus this child has a
discrepancy between his achievement level in reading/writing/math and his IQ
score. The child is learning disabled if
we can't explain his low achievement better with one of the excluding factors
(a sensory problem like poor vision, intellectual disability, emotional or
behavioral problems, lack of motivation, insufficient instruction, poor English
proficiency and so on). If one of these
excluding factors explains the child's poor achievement better, the main cause of
his difficulties is probably not learning disability.
According to the
IQ-achievement discrepancy model, LD is a situation in which the child has specific
cognitive deficits that lower his reading/writing/math achievement, but due to
his average intellectual ability, the child has a good chance to withstand the disability or "bypass" it. Such a child may have trouble with reading
comprehension because he reads slowly and inaccurately, but may be able to
understand the same text well if it is read to him.
According to the
IQ-achievement discrepancy model, LD is not a situation in which a child
has many poor cognitive abilities. Such
broad deficits usually lower the general intelligence score. A child with many poor cognitive abilities
will find it hard to "bypass" his difficulties. Such a child may have trouble with reading
comprehension because he reads slowly and inaccurately, but may also find it
difficult to understand the same text if it is read to him. That's because his general and lexical knowledge,
abstract thinking and deduction abilities may also be poor and lower his
listening comprehension.
Prof.
Tannock writes:
"The logic behind the IQ-discrepancy
definition is that the cause of the learning difficulties would differ between
those with and without IQ-Achievement discrepancy".
I think the same cognitive
disabilities can cause problems in acquiring reading/writing/mathematics both
with people with (at least) average IQ (people with discrepancy) and with
people with an IQ score lower than average (people without a discrepancy). The difference between the groups is that
people without a discrepancy have more cognitive deficiencies/disabilities
than people with a discrepancy. The
reason for that is simple: the general
IQ score is comprised of a person's scores in the various cognitive
abilities. The more poor abilities a
person has, the lower is his IQ score. This
quantitative difference (a child having many poor abilities) makes a
qualitative difference in the ability to learn and problem solve.
"Thus, we sought evidence to support
or refute the notion that individuals with learning difficulties with and
without an IQ-achievement discrepancy differ in clinically meaningful ways…"
"..numerous
studies (e.g., Fletcher et al., 2005; Francis et al., 2005; Siegel, 1992) and meta-analyses (Hoskyn,
2000; Maehler &
Schuchardt, 2009; Stuebing et al., 2002) have been conducted to test for
differences between discrepant and non-discrepant groups of children with LD in
terms of cognitive processes that contribute to learning. Findings are
consistent: the two groups do not differ
in their cognitive processing skills".
I looked at some of the
papers cited here. The Maehler &
Schuchardt, 2009 study, for instance, is not a
"meta-analysis". This research
compared between three groups of children in grades 2 to 4. Each group had 27 children (a minimal group
size for acceptable statistical results is 30, if I'm not mistaken).
In the control group the
children did not have reading difficulties. In the other two groups the
children had significant reading difficulties.
The children in one of the
reading difficulty groups had an "IQ-achievement discrepancy". The children in the other reading difficulty
group did not have such a "discrepancy".
The authors found that the
control group children's working memory was higher than that of both reading
difficulty groups.
Another finding was that
there were no differences in working memory between the "no
discrepancy" and the "discrepancy" groups. This finding is cited by Prof. Tannock as
supporting the argument that the IQ-achievement criterion is not suitable for
LD diagnosis.
A closer look at this study
shows that the children were assigned into the "no discrepancy" and
"discrepancy" groups not according to their IQ score but according
to…the simultaneous processing index of the KABC test. Almost all tests in this index (except matrix
analogies) measure visual processing in tems of CHC abilities (Alfonso et al, 2005). Thus, the children were assigned to "no
discrepancy" and "discrepancy" groups not by their IQ scores but
according to their visual processing scores.
Thus it can't be concluded
from this research that there's no difference in working memory between
children with and without IQ-achievement discrepancy.
What can be concluded is
that among children with poor reading there is no difference in working memory
between children with average visual processing and children with poor visual
processing. And why would there be? Children with good visual processing will
not always have good working memory as well.
Although both working memory and visual processing are parts of general
intelligence, and there should be a positive correlation between them, the size
of the correlation may be too low to cause a significant difference between the
groups in working memory.
Why is the working memory
of the reading difficulty groups poorer than that of the control group of
children without reading difficulties?
Since short term memory may be one of the causes of reading
difficulties.
Prof. Tannock further
writes:
".. our review of studies of
predictive validators also failed to find robust evidence of difference between
those with and without an IQ-achievement discrepancy. The groups do not differ
in long-term prognosis, nor do they differ in terms of response to intervention."
It would be interesting to
read the papers which looked at the long term prognosis. Is it long term prognosis of reading or of
the child's general wellbeing? It's
reasonable to assume that a child with reading difficulties and high IQ, say
120, will have a better educational and vocational outlook than a child with
reading difficulties and low IQ, say 75.
Our review of literature from the past
two decades concurred with several previous reviews: there is no robust
evidence to support the validity of this criterion. The criterion is
conceptually and statistically flawed.
The IQ-achievement discrepancy
criterion has its disadvantages (for example "wait to fail" in young
children; adolescents failing to achieve a discrepancy despite being leaning
disabled). Abandoning this criterion
because of the argument that there is no difference in cognitive processing
between children with and without a discrepancy or because of the argument that
children with and without a discrepancy have the same long term prognosis – is
not serious in my opinion.
The Work-Group reviewed the literature to
seek validation of three major approaches that have been proposed:
i)
inclusion of cognitive processing deficits (e.g., Hale, 2010; Kavale & Forness,
2000); Hale 2010 is an expert white paper consensus
written by 58 of the best researchers in the LD field. They agreed that "To meet SLD statutory
and regulatory requirements, a “third method” approach that identifies a
pattern of psychological processing strengths and weaknesses, and achievement
deficits consistent with this pattern of processing weaknesses, makes the most
empirical and clinical sense".
ii) ‘response-to-intervention’ criterion
(e/g. US Department of Education, 2004; Vaughn & Fuchs, 2003);
and iii) augmentation of the
low-achievement-for-age component of the DSM-IV criterion (e.g., Dombowski et
al., 2004; Tumney & Greaney, 2009).
I'll write here only about the
first suggested criterion (Prof. Tannock writes about all three).
Cognitive processing deficits as a possible
diagnostic criterion
The underlying premise is that various
cognitive (psychological) processing deficits play a causal role in SLD and
therefore would serve as valid indicators of SLD. The presumption of underlying
cognitive processing deficits is part of the IDEA (2004) definition of SLD, and
this approach is strongly supported in the field of neuropsychology as well as
by advocacy groups (e.g., Hale et al., 2010).
Prof. Tannock describes
critique of this approach and then presents the results of the literature
review of the work group concerning this issue.
One major critique of this approach is
that ‘processing deficits’ are rarely measured directly, but inferred from
scores on various neuropsychological tests, which in turn measure a complex web
of cognitive, behavioral, and motivational processes. This
is true. We can't get every child into a
brain scanner.
A second major critique is the limited
empirical support for the inclusion of cognitive processing deficits in the
diagnostic criteria for SLD. For instance although a meta-analysis found
moderate to large effect sizes for differences in cognitive processing between
children with SLD and typical development, there was no evidence that cognitive
deficits contributed to differential diagnosis of SLD).
It's
true that a person who has a cognitive disability does not necessarily have
LD. A person can have poor visual-spatial
processing, for example, and will find it difficult to navigate to new
places. But he may read, write and do
math well. A person who has good
reading/writing/math is not learning disabled.
Thus a specific cognitive disability is not a sufficient criterion for
LD. But many researchers think that a
specific cognitive disability is a necessary criterion for LD. IDEA 2004 is written according to this view.
Cognitive processing skills cannot be
used to rule in or rule out a diagnosis of RD, because the relationship between
the cognitive processing skills and reading skill is probabilistic and not
deterministic (i.e., not diagnostic).
By
contrast, the Work-Group’s review of the literature on predictive validators
revealed quite strong support for the inclusion of cognitive processing
deficits as a diagnostic criterion for SLD. For
example, several studies report that measures of cognitive processing skills
associated with reading (e.g., phonological awareness, naming speed) predicted
response to intervention in children with RD (Al Otaiba & Fuchs, 2002;
Frijters et al., 2011); Fuchs et al., 2012).
However, counter arguments include:
i)
cognitive deficits associated with RD are not unique to this disorder but are
shared with other neurodevelopmental disorders, such as ASD, ADHD, and
developmental coordination disorder (e.g., Willcutt et al., 2010);
ii) cognitive processing deficits that
underlie other manifestations of SLD
(mathematics, written expression) remain unclear (Geary, 2010; Ramus
& Hissar, 2012);
and iii) the required assessment of
cognitive processing skills may be prohibitively expensive and waiting lists
are often long (Compton et al., 2012).
Thus the Work-Group ruled out cognitive
processing deficits as a possible diagnostic criterion for SLD based on
consideration of its empirical evidence and clinical utility.
That's too bad! I find the last three counter arguments
un-persuasive. In doing so, the work
group has weakened LD diagnostic criteria in DSM5. The new criteria widen the boundaries of the
LD group to include people who are not LD.
Children who have average
achievement in reading/writing/math can be learning disabled according to DSM5
if their achievement "is sustainable only by extraordinary high levels of
effort or support". Thus LD is
diagnosed according to subjective judgement of the extent of effort that
the child invests to reach average achievement.
Admittedly, this has nothing to do with the cognitive ability criteria.
On the other end of the
scale, children with an IQ score of, say, 66, can also be diagnosed as LD
according to DSM5, although clearly their reading/writing/math difficulties are
caused by many cognitive disabilities that lower their general intelligence and
significantly interfere with everyday academic and other functioning. These are "SLOW LEARERS" in
Flanagan's conceptualization. These are
not children with a specific cognitive disability that interferes with learning
in a limited way, as LD children are meant to be.
The inclusion of these
groups causes improper spending of funds.
Slow learners need much more financial resources than LD children or
children who have "average achievement sustainable by high levels of
effort or support".
Alfonso,
V. C., Flanagan, D. P., & Radwan, S. (2005). The impact of the
Cattell-Horn-Carroll theory on test development and interpretation of cognitive
and academic abilities. Contemporary intellectual assessment: Theories,
tests, and, (2nd), 185-202.
Maehler C, Schuchardt K.(2009). Working memory
functioning in children with learning disabilities: does intelligence make a
difference? J Intellect Disabil Res.53(1):3-10
http://www.nnce.org/Arquivos/Seminarios/2009.1/04-Abril/luciana_dias_pdf_0901.1_abr.pdf
